1. Field of the Invention
The present invention relates to a cylindrical waveguide to be used, for example, as a satellite broadcast transmitting and receiving antenna for the transmission and reception of a polarized wave.
2. Description of the Related Art
A satellite broadcast receiving converter using a conventional cylindrical waveguide will be described below with reference to FIGS. 8 and 9, of which FIG. 8 is an exploded perspective view of the conventional converter and FIG. 9 is an explanatory diagram for explaining a bent portion of a cavity in the cylindrical waveguide of the conventional converter.
As shown in FIGS. 8 and 9, a body member 31 formed by aluminum or zinc die casting comprises a cylindrical waveguide 32 for introducing a polarized wave and a housing 41 for receiving a circuit portion therein, the cylindrical waveguide 32 and the housing 41 being formed integrally with each other.
The cylindrical waveguide 32 has a first cylindrical waveguide portion 34 having a horn portion 33 for introducing a polarized wave, a second cylindrical waveguide portion 35 disposed perpendicularly to the first waveguide portion 34, and a cylindrical connection 36 which connects the first and second waveguide portions 34, 35 with each other and which is bent 90xc2x0. As depicted in FIG. 9, centrally and axially of the first waveguide portion 34 is formed a first cavity 37 which is straight, and also formed centrally and axially of the second waveguide portion 35 is a second cavity 38 which is straight. The first and second cavities 37, 38 are connected with each other through a 90xc2x0-bent cavity 39 which is formed in the connection 36 to form a cavity 40. Inside the horn portion 33 is formed a first opening 40a which opens one end of the cavity 40 as shown in FIG. 8. The opposite end side of the cavity 40 is also open.
Returning to FIG. 8, the housing 41, which is formed of the same material as the cylindrical waveguide 32, has a bottom wall portion 41a, a side wall portion 41b which is formed upright so as to enclose the bottom wall portion 41a, and a receptacle portion 41c which is open above the side wall portion 41b and which is enclosed with the side wall portion 41b. Near one end side of the bottom wall portion 41a is formed a second opening 41d which is an opposite end-side opening of the cavity 40.
On both upper and lower sides of a single rectangular circuit board 42 constituted by an insulating board are formed annular earth electrodes 43 as soldered layers each having about the same diameter as the second opening portion 41d. A large number of through holes 43a extending vertically through the circuit board 42 are formed in both upper- and lower-side earth electrodes 43 to connect the earth electrodes with each other.
A first probe 44 for catching a vertically polarized wave is formed by a conductive pattern longitudinally of the circuit board 42 from near the center of the earth electrode 43 formed on the upper side of the circuit board. On the other hand, in the transverse direction of the circuit board 42 is formed an L-shaped, second probe 45 by a conductive pattern to catch a horizontally polarized wave. One ends of the first and second probes 44, 45 are connected to an electric circuit (not shown) formed on the upper surface of the circuit board 42. The circuit board 42 is placed on a stepped portion located near the bottom wall portion 41a out of plural stepped portions (not shown) formed inside the housing 41 and is fixed to the housing by a suitable means. At this time, the earth electrode 43 formed on the lower side of the circuit board is grounded to the bottom wall portion 41a while surrounding the second opening 41d formed in the housing 41.
A generally square, bottomed, metallic case 46 is attached to the circuit board 42 so as to cover the earth electrode 43 formed on the upper side of the circuit board 42, by a suitable means such as the use of screws. An inside bottom (not shown) of the metallic case 46 functions as a short-circuit surface for the first and second probes 44, 45.
A cover 47 constituted by a single rectangular metallic plate is placed on a stepped portion (not shown) located on a remote side from the bottom wall portion 41a of the housing 41 and is fixed by a suitable means. The receptacle portion 41c of the housing 41 is sealed hermetically and the interior thereof is held in an electrically shielded state.
A more detailed description will now be given about the cavity 40 of the cylindrical waveguide 32. As shown in FIG. 9, the first and second cavities 37, 38 are each formed at a diameter of D1, and on the innermost side of the cavity 40 when seen sideways of the body member 31, the cavities 37 and 38 are constituted by an innermost wall portion 37a of the fist cavity 37, an innermost wall portion 38a of the second cavity 38, and an inner bent portion 39a as an innermost wall portion of the cavity 39 in the connection 36 which connects the first and second cavities 37, 38 with each other. On the outermost side of the cavity 40, the first and second cavities 37, 38 are constituted by an outermost inner wall portion 37b of the first cavity 37, an outermost inner wall portion 38b of the second cavity 38, and an outer bent portion 39b as an outermost inner wall portion of the cavity 39 in the connection 36.
The inner bent portion 39a has a quadrant circumference described with a radius of R2 which is three times as long as the diameter D1 from a central position C4, the central position C4 lying on a 45xc2x0 line Z1xe2x80x94Z1 at an intersecting point of an extension line X1 of the innermost wall portion 37a of the first cavity 37 and an extension line Y1 of the innermost wall portion 38a of the second cavity 38. The innermost wall portions 37a and 38a of the first and second cavities 37, 38 are connected together at the radius R2. The outer bent portion 39b has a quadrant circumference described at a radius of R3 which is four times as long as the diameter D1 also from the central position C4. The outermost inner wall portions 37b and 38b are connected with each other at the radius R3.
In the satellite broadcast receiving converter using the conventional cylindrical waveguide, however, the central position of the radius R2 of the inner bent portion 39a of the cavity portion 39 in the connection 36 and the radius R3 of the outer bent portion 39b of the cavity 39 are the same and the radii R2 and R3 are respectively three and four times as long as the diameter D1, so that the cavity 39 is large in the directions of the extension lines X1 and Y1, with consequent increase in size of the connection 36, thus giving rise to the problem that the cylindrical waveguide 32 becomes larger in size.
It is an object of the present invention to provide a cylindrical waveguide which has a low reflection characteristic and which is small in size.
For achieving the above-mentioned object, according to the present invention, in the first aspect thereof, there is provided a cylindrical waveguide comprising a first waveguide portion having a cylindrical cavity, a second waveguide portion disposed perpendicularly to the first waveguide portion and having a cylindrical cavity, and a connection connecting the first and second waveguide portions with each other and having a bent cylindrical cavity, wherein an inner bent portion of an inner wall portion in the cavity of the connection connects the cavities of the first and second waveguide portions with each other on a bent right-angle side and at a first radius from a first central position, while an outer bent portion of the inner wall portion in the cavity of the connection connects the cavities of the first and second waveguide portions with each other on the bent right-angle side and at a second radius from a second central position, and the inner bent portion connects the cavities of the first and second waveguide portions with each other in a range of not larger than one-fourth of the diameter of the cavities on each of an extension line of the innermost wall portion in the cavity of the first waveguide portion and an extension line of the innermost wall portion in the cavity of the second waveguide portion, from an intersecting point of both extension lines.
In the second aspect of the present invention, the radius from the first central position is set zero, and the cavities of the first and second waveguide portions are connected perpendicularly to each other by the inner bent portion of the inner wall portion in the cavity of the connection.
In the third aspect of the present invention, the radius from the second central position is set 1.5 to 5 times as large as the cavity diameter, and the cavities of the first and second waveguide poritons are connected with each other by the outer bent portion of the inner wall portion in the cavity of the connection.
In the fourth aspect of the present invention, the first and second central positions lie on a 45xc2x0 line which bisects the right-angled bent side.